Process for treating polyethylene film



PROCESS non TREATING POLYETHYLENE FILM John C. Elliott, Madison, Wis.,assignor to Bjorksten Research Laboratories, Inc., a corporation ofIllinois 3 Claims. (Cl. 117-118) This invention pertains to film ofpolymerized hydrocarbons, and particularly to a method for removing thewaxy surface feel of polyethylene and its analogues.

This application is a continuing application of applica- I tion SerialNo. 190,053, filed October 13, 1950, now abandoned.

The polyethylene films have gained considerable acceptance because oftheir relatively low cost, high tenacity, resiliency, resistance towater and other desirable film properties. They have met with.considerable sales resistance however, because of a waxy or greasysurface feel, which is disagreeable to many persons.

' An object of this invention is to overcome this greasy surfacecharacteristic, and to provide polyethylene films which havesubstantially the same non-greasy feel, as for example the vinyl films,without loss of any of their desirable properties.

Further objects will become apparent as the present detailed descriptionproceeds.

In accordance with my invention, I expose the poly- V ethylene film tobe treated to the action of chlorine under oxidizing conditions. Forexample, passing the film through a bath of aqua regia is suitable,although other treatments exposing the film to the oxidative influenceof nitrosyl chloride, or of a chlorine oxide, are also suitable.

For practical reasons I prefer to apply the treatment in a liquid bath,under conditions providing for ample ventilation, though a vaportreatment is also possible.

The invention is further illustrated by the following specific examples,which are given to illustrate the invention only, and are not to beconstrued in any sense of limitation.

Example 1 I I pass a polyethylene film through a bath containing %-40%of fuming nitric acid and 60%80% of 38% commercial hydrochloric acid ata rate of speed which leaves the film in contact with the said bath for60 seconds, the bath having a temperature of 65 C. As the film leavesthe bath, it is impinged upon with air currents from air jets on bothsides, the apertures of the jets having a diameter of approximately 0.01inch and the air pressure being approximately 40 pounds per square inch.These air jets blow any adherent drops of acid away from the film andback into the acid bath. The film is then passed through a water sprayand then through ammonium hydroxide to neutralize the acid, and is thendried either by blowing off the remaining adherent water drops with airjets, or by festooning, or by an air tunnel, or in any 7 other of themany ways well known to the art.

The film, after this treatment, has lost its waxy or greasy feel.

ice

Example 2 I pass a polyethylene film through a vapor space filled withvapors of nitrosyl chloride, at a temperature ofx 60 C., the time ofcontact being 2 minutes. The film is then passed through a water bath,containing a trace of sodium carbonate, ammonia, soap or the like toneutralize residual acidity, and is then blown dry ordried. The filmthus treated has a substantially non-greasy feel.

'While referencehas been made in the above to specific embodiments ofthe invention, the process and products are by no means restrictedthereto.

While I do not wish to commit myself to any theory regarding the causeof the results obtained by my process and the properties of theresultant product, it is my belief that the greasy feel of ordinarypolyethylene film is due to the presence of side chains in the polymer,and that the treatrnent, disclosed eliminates these by an oxidativeprocess, while leaving the continuous chains intact.

Accordingly, the treatment is not strictly confined to polyethylene, butwill apply likewise to other hydrocarbon resins, which gave a greasy"feel due to the presence of side chains. The strong oxidative treatmentcan be accomplished with aqua regia, chlorine monoxide, chlorinedioxide, or nitrosyl chloride, aqua regia being the preferred treatment.The corresponding compounds of other halogens may also be employed.

The temperature of the treatment can be varied up to the temperatures atwhich the polyethylene softens, to the At low' extent that it becomesinconvenient to handle. temperatures, the time required for treatmentincreases, but even room temperatures and lower can be employed if thetime of treatment is accordingly lengthened, for. example, 24 hours fortreatment at 0 C. The mechanical details of applying the treatment, ofremoving excess agent, and of drying are well known in the art ofchemical engineering.

It is thus seen that the invention is capable of wide variations, andthat the invention is not to be limited excepting by the claims, inwhichit is my intention to cover all novelty inherent in the inventionas broadly as possible in view of prior art.

Having thus disclosed my invention, I claim:

1. The process for treating polyethylene film which consists ofsubjecting the surface of polyethylene film to the action of a liquidmixture consisting of 20 to 40% of fuming nitric acid and 60 to 80% ofcommercial hydrochloric acid to form a superficially chlorinatedpolyethylene surface.

2. The process for treating polyethylene film which consists ofimmersing polyethylene film in a liquid mixture consisting of 20 to 40%of fuming nitric acid and 60 to 80% of commercial hydrochloric acid.

3. The process for treating polyethylene film which consists ofimmersing polyethylene film in a liquid mixture consisting essentiallyof 25% of concentrated nitric acid and of concentrated hydrochloricacid.

References Cited in the file of this patent UNITED STATES PATENTS HortonFeb. 2, 1954

1. THE PROCESS FOR TREATING POLYETHYLENE FILM WHICH CONSISTS OFSUBJECTING THE SURFACE OF POLYETHYLENE FILM TO THE ACTION OF A LIQUIDMIXTURE CONSISTING OF 20 TO 40% OF FUMING NITRIC ACID AND 60 TO 80% OFCOMMERICIAL HYDROCHLORIC ACID TO FORM A SUPERFICIALLY CHLORINATEDPOLYETHYLENE SURFACE.